Solar panels are in increasingly widespread use in the generation of electricity. The outputs therefrom may be used directly in driving other devices, or may be used in charging electrical storage means or in supplying power to the mains electricity network. As the output of a solar panel varies, non-linearly, depending upon, for example, the intensity of the light incident thereon, the operating temperature, and other factors, the direct, uncontrolled supply of the output from the solar panel to a load is usually inappropriate. FIG. 1 illustrates, diagrammatically, a typical I-V output of a solar panel under a range of incident light intensities, showing the relationship between the generated current and the associated output voltage. The maximum power output occurs if the circuit, of which the solar panel forms part, is operating on the line 10 in FIG. 1. Clearly, as the light intensity changes, the operating current and voltage required for the maximum output vary. In order to ensure that the solar panel and associated circuit operate at around the point of maximum power, a maximum power point tracking algorithm is used. The output of the maximum power point tracking algorithm is used in varying the load supplied by the solar panel, for example switching in or out resistances thereof, in an attempt to maintain the operation of the solar panel at around its optimum point.
In some older systems the algorithm operates to ensure that the circuit operates at 70% of the open circuit voltage. This is achieved by repeatedly and rapidly connecting disconnecting the supply, ie the output from the solar panel, from the load. By way of example, the supply may be connected and disconnected in the region of 1000 to 3000 times per second. By disconnecting the output for a proportion of the time in this manner, the duty cycle is reduced, for example to around 70% as mentioned above.
Whilst such a system may operate satisfactorily in some circumstances, when the supply is disconnected there is no output from the panel to the load and consequently, even if the panel would otherwise be operating at the maximum power point, potential power is being lost whilst the panel is disconnected. The arrangement is therefore less efficient than it could be.